Field of the Invention
The invention concerns a method of starting up a thermoreactor arranged in an exhaust gas flow from an internal combustion engine, wherein combustion gas is ignited by spark ignition in at least one cylinder of the internal combustion engine and the exhaust gas resulting from combustion of the combustion gas is at least partially fed as an exhaust gas flow to the thermoreactor.
Description of Related Art
Methods of exhaust gas post-treatment are frequently used to comply with the emission limit values of internal combustion engines. A method which is also known from the field of exhaust gas post-treatment of caloric power plants is regenerative thermal oxidation (RTO) in which unburnt hydrocarbons and other oxidisable exhaust gas constituents are thermally oxidised. In regenerative thermal oxidation, the exhaust gas is firstly passed by way of a heat storage means generally comprising ceramic loose material or honeycomb bodies in order finally to pass into the reaction chamber. In the reaction chamber, the exhaust gas is further heated by additional heating devices until thermal oxidation of the unwanted exhaust gas constituents can take place. The exhaust gas then flows through a further heat storage means to the exhaust pipe and is discharged into the environment. In operation, the flow direction is alternately altered whereby the exhaust gas is pre-heated before reaching the reaction chamber, thereby achieving an energy saving in further heating of the exhaust gas. The additional heating effect can be implemented by gas injection or burners (so-called support gas) or an electrical additional heating device. The reaction chamber generally has a free flow cross-section whereby the residence time of the exhaust gas in the reaction chamber is increased and oxidation can take place in the form of a gaseous phase reaction. Carbon monoxide (CO) and methane (CH4) are particularly relevant among the species to be oxidised in the exhaust gas.
Such an arrangement is known, for example, by the trade name CL.AIR® from GE Jenbacher. In that method, exhaust gas is heated to about 700-800° C. and oxidation of the unburnt hydrocarbons and the carbon monoxide is effected to give water vapor and carbon dioxide. The CL.AIR® thermoreactor is in the form of a regenerative heat exchanger and comprises two storage masses, a reaction chamber and a switching-over mechanism. The exhaust gas flows coming from the engine at a temperature of about 530° C. by way of a switching-over mechanism into a first storage mass where it is heated to approximately 800° C. In the reaction chamber, the exhaust gas reacts with the oxygen present, in which case carbon monoxide and unburnt hydrocarbons are oxidised to give carbon dioxide and water. When flowing through the second storage mass, the exhaust gas again gives off heat and is at a temperature of between 550 and 570° C. when reaching the switching-over mechanism which passes it to the chimney or a downstream-disposed exhaust gas heat utilisation arrangement.
A disadvantage with solutions known from the state of the art is that, during the engine start-up phase, when therefore the thermoreactor has not yet reached its operating temperature, oxidisable species are emitted to an undesirably high extent.